A piezoelectric element becomes deformed upon receipt of supplied electric energy and is widely used as, e.g., a liquid ejection head, a micropump, or a drive element for use with a sound-generating member (a speaker or the like). Here, the liquid ejection head ejects droplets from nozzle orifices by inducing pressure fluctuations in liquid stored in a pressure chamber. For instance, the liquid ejection head includes a recording head used in an image recording apparatus such as a printer, a liquid-crystal ejection head used in manufacturing a liquid-crystal display, and a coloring material ejection head used in manufacturing a color filter. The micropump is a ultra-compact pump capable of pumping a trace amount of liquid and used at the time of, e.g., delivery of a trace amount of chemical.
One important component used in such a liquid ejection head or a micropump is a piezoelectric actuator having a piezoelectric element provided on the surface of a diaphragm. The piezoelectric actuator is attached to a pressure chamber formation substrate having a void which serves as a pressure chamber, thereby partitioning a part of the pressure chamber with the diaphragm. At the time of ejection of droplets or delivery of liquid, a drive pulse is supplied to the piezoelectric element in order to deform the piezoelectric element and the diaphragm (e.g., a deformation portion of the pressure chamber), thereby changing the volume of the pressure chamber.
In relation to the liquid ejection head or the micropump, strong demand exists for high-frequency actuation of the piezoelectric element. This is intended for implementing high-frequency ejection of droplets or improving liquid delivery capability. In order to implement high-frequency actuation of the piezoelectric element, compliance of the deformation portion must be made smaller than that of a conventional piezoelectric element, and the amount of deformation of the piezoelectric element must be made greater than that employed conventionally. The reason for these measures is that a reduction in compliance of the deformation portion leads to an improvement in responsiveness. The piezoelectric element can be actuated at a frequency higher than a conventional frequency. Further, an increase in the amount of deformation of the piezoelectric element leads to an increase in the amount of volumetric change in the pressure chamber. Hence, the quantity of droplet to be ejected and the quantity of liquid to be delivered can be increased.
A piezoelectric element of multilayer structure has been proposed as an element which satisfies mutually contradictory characteristics; that is, the compliance of the deformation portion and the amount of deformation of the piezoelectric element. For instance, there has been put forward a piezoelectric element having a structure in which the piezoelectric layer is formed into a two-layer structure; that is, an upper piezoelectric body and a lower piezoelectric body, and in which a drive electrode (individual electrode) is formed at a boundary between the upper piezoelectric body and the lower piezoelectric body. Further, a common electrode is formed on an exterior surface of the upper piezoelectric body and an exterior surface of the lower piezoelectric body (as described on, e.g., Japanese Patent Publication No. 2-289352A, page 6 and FIG. 5; and Japanese Patent Publication No. 10-34924A, page 5 and FIG. 9).
Since the piezoelectric element of multilayer structure has a drive electrode provided at a boundary between the upper piezoelectric body and the lower piezoelectric body, the respective layer piezoelectric bodies are provided with electric fields whose intensities are defined by intervals between the drive electrode and the respective common electrodes (i.e., the thicknesses of the respective layer piezoelectric bodies) and potential differences between the drive electrode and the respective common electrode. Therefore, when compared with a piezoelectric element of a single layer structure having a single layer of piezoelectric body sandwiched between the common electrode and the drive electrode, the piezoelectric element can be deformed greatly with the same drive voltage as a conventional drive voltage even when the thickness of the entire piezoelectric element is increased slightly and the compliance of the deformation portion is reduced.
However, acquisition of a characteristic which can respond to a recent high level of demand cannot be achieved by mere use of the piezoelectric element of multilayer structure. For this reason, there is no alternative but to use, as an actual product, a piezoelectric element of single structure in which a single layer of piezoelectric body is sandwiched between the common electrode and the drive electrode. This failure can conceivably be attributed to various reasons, including insufficient stability of deformation in a piezoelectric element and the amount of deformation of the piezoelectric element, as well as insufficient manufacturing efficiency and insufficient reliability of a product.